both 课间休息 and 下课 are okay 课间休息 more likes a noun while 下课 more likes a verb You can say"现在下课" which means now you can have a class break

We usually say"你們 中間 下課 是 什麼時候?" Explanation: 你們=your，下課=class break，是=is，什麼時候=When， Here, We use "中間" to describe "between classes" ，so "中間" is the adjective to describe classes and we put it right in front of "下課".

simple answer: chinese commonly say 'when is the class over' or 'how long is it from the class break' instead of 'when is your class break' even you can ask like that as well. people can still get the meaning but it feels like a "bump" in the road because Chinese doesn't work that way.

We say 下課 for the class break, but it could also means the end of all classes today. If you know which class, you can be more specific, for example 第1堂下課